1. Field of the Invention
This invention relates generally to the metal-forming arts, and more particularly to a system for measuring and controlling the flow of molten metal into a casting mold.
2. Description of the Prior Art
In the metal forming arts, it has long been an objective to control the flow rate of molten metal into a casting mold to provide in some instances a constant flow rate and in other instances a variable flow rate to properly fill the narrow and wide sections of the mold and to control the flow according to the mold shape. The flow rate has been controlled by providing a corresponding level of metal in the casting tundish, or by providing flow control devices in the pouring spout of the tundish. Frequently a holding furnace was provided between the melting furnace and the tundish to properly maintain and control the level in the tundish. The holding furnace has been automatically controlled to pour metal into the tundish at a rate to maintain the desired metal level therein. Flow rate control was particularly acute in continuous casting operations where an improper flow rate can reduce capacity, increase the number of unacceptable castings, and increase scrap rate due to surface imperfections, tears, pin holes, internal tears, and buttend scrap.
Other causes of high scrap rate are short pours, wherein insufficient metal is poured into the mold resulting in an incomplete molded part; long pours, wherein metal is wasted and difficulty in separating sand molds is experienced due to the excess metal solidifying on the mold exteriors; intermittent pours, wherein a "marble" effect occurs due to irregular cooling of the metal; and mold blow out wherein the mold walls are disrupted due to excessive pouring rates.
Numerous efforts have been made to measure the metal flow and control the pour. Such efforts are exemplified by the devices disclosed in the following U.S. Pat. Nos.:
3,478,808 PA1 3,528,479 PA1 3,537,505 PA1 3,838,730 PA1 3,842,894 PA1 3,875,989 PA1 3,884,288 PA1 3,942,577 PA1 3,961,662 PA1 4,014,379 PA1 4,030,531 PA1 4,050,503 PA1 4,077,457
These efforts have included irradiating the molten metal stream and measuring the affect of the stream on the radiation; flowing the stream through a magnetic field of the stream; and measuring the light emission of the stream with a photoelectric cell. All of these methods were inexact and only approximate. It was difficult, if not impossible, to obtain sufficiently accurate flow data to be useful in a pour-casting process. Further, many prior efforts have involved apparatus which is required to be relatively closely positioned to the flow stream for proper operation. This has the disadvantage of subjecting the apparatus to extremely high temperatures and also subjecting it to contact with the molten metal which in most cases would disable the measuring apparatus.